Biology subjects

Londono, G. A.

Publications and source records attributed to Londono, G. A..

3 recordsLinked to original sources

bioRxiv2025

Tropical montane and temperate hummingbirds incubate in small installments over long periods

Life-history strategies and development are shaped by climate and predation. We examined how temperature and nest survival drive incubation behavior in 104 nests of 34 hummingbird species across 2,939m of elevation in the Peruvian and Colombian Andes. At high elevations, cold temperatures led to more frequent, brief incubation bouts and extended incubation periods; survival modulated incubation behavior with no effect on development. Hummingbirds had the highest egg surface-area to volume ratios among all birds; in 147 species, incubation periods increased with decreasing ambient temperatures. We propose a new hypothesis to explain how in cold conditions, heat transfer to the embryo is fragmented into smaller increments and therefore extended over longer periods, underscoring the role of adult behavior in mediating embryonic temperature mismatches and life-history tradeoffs.

ecology↗

bioRxiv2022

Ecological drivers and evolutionary consequences of torpor in Andean hummingbirds

Daily torpor allows endotherms to save energy during energetically stressful (e.g., cold) conditions. Although studies on avian torpor have mostly been conducted under laboratory conditions, information on the usage of torpor in the wild is limited to few, predominantly temperate-zone species. We studied torpor under seminatural conditions from 249 individuals from 29 hummingbird species across a 1,920 m elevational gradient in the western Andes of Colombia using cloacal thermistors. Small birds used torpor more often than large birds, but only at low ambient temperatures, where torpor was prolonged. We also found effects of proxy variables for body condition and energy expenditure on the use of torpor, its characteristics, and impacts. Our results suggest that judicious deployment and subtle modifications of torpor, as well as phylogenetic variation in propensity for torpor, have allowed only certain clades of hummingbirds to colonize and persist in the harsh climate of the high Andes.

ecology↗

bioRxiv2022

Adaptive variation in avian eggshell structure and gas conductance across elevational gradients?

Many tropical species have restricted elevational distributions, which are potentially bounded by constraints imposed by physical conditions on physiological processes. Although some studies have examined variation in the physiology of adult birds with respect to elevation, little attention has been paid to the structure and function of eggshells, which mediate gas exchange between the embryo and the environment. At high elevations, dry air is expected to increase water loss from the egg; selection to avoid desiccation might therefore be expected to favor reduced gas conductance by means of increased eggshell thickness or reduced pore size. We used gas diffusion experiments and scanning electron microscopy to examine water vapor conductance rates and eggshell structures in 197 bird species distributed along an elevational gradient in the Andes. As predicted, water vapor conductance across the eggshell declined in a narrow range with elevation among all species and among species within families, but not among individuals within species. Variation among species in eggshell conductance was lower at high-elevation sites, potentially indicating greater constraints at such sites. Structural changes in eggshells with respect to elevation varied among taxonomic families of birds, suggesting potentially different adaptive responses to common selective pressures in terms of eggshell thickness and pore density, and size. We suggest that considering functional and structural traits of eggshells, which influence embryo development, may help one to better understand the elevational distributions of species and to forecast their responses to global climate change.

evolutionary biology↗